This invention deals generally with heat sinks for cooling electronic devices such as pumped lasers and integrated circuits, and more specifically with a heat spreader constructed so that solder spreading from holes into which heat pipes are inserted does not affect the nearby thermal transfer surface which contacts the electronic device.
As electronic devices are becoming more powerful, the task of removing heat from them is becoming more critical. In many situations the heat flow resistance between an electronic device, such as a pumped laser or an integrated circuit, and the heat spreader which removes heat from it accounts for a significant portion of the total thermal resistance in the device's cooling system. Since greater thermal resistance causes the device to run hotter for any given heat spreader temperature, it is very important to assure that the surface on the electronic device and the thermal contact surface of the heat spreader are kept as clean and as flat as possible to assure that the very best thermal conductivity is maintained between them.
However, even when a heat spreader is itself manufactured with a flat thermal contact surface, the thermal contact surface can be dramatically affected by the processes involved in attaching the heat spreader to the rest of the cooling assembly.
A typical electronic device cooling assembly in use today has very few major parts. One or more heat pipes are attached to the heat spreader, and the heat pipes are also attached to a heat removal device such as an assembly of cooling fins in order to transfer heat to the ambient air. Since the external structure of a typical heat pipe is a simple tube sealed at both ends, the method of attaching the heat pipe to the heat spreader is usually to drill long cylindrical holes into the plate-like heat spreader from one edge. The heat pipes are then attached within the holes of the heat spreader by inserting solder into the holes before the heat pipes are inserted, and then heating the entire assembly, while it is oriented with the heat pipes vertically above the heat spreader, so that the solder bonds the heat pipes to all the interior surfaces of the holes in the heat spreader. The heat pipes are then attached to the cooling fin assembly by epoxying the heat pipes into slots in the base plate of the fin assembly.
However, the process of soldering the heat pipes into the heat spreader causes a problem. Since it is important to use sufficient solder to bond the heat pipes to the entire inside surface of each deep hole in the heat spreader, and it is difficult to control the flow of solder or the creation of bubbles during the process, solder sometimes flows out of the holes and onto the nearby thermal contact surface of the heat spreader. This excess solder attached to the thermal contact surface of the heat spreader destroys its value, and the solder must either be removed or the assembly discarded. Either choice adds significantly to the cost of manufacture, and it would be very advantageous to have an electronic device cooling assembly in which the heat spreader thermal contact surface was protected from excess solder used to bond the heat pipe to the heat spreader.